It will be attempted to develop a radiopharmaceutical labeled with I123 for adrenal imaging for possible human application which is safer than the one currently employed. 19-iodocholest-5-en-3 beta-o1 (19-iodocholesterol) labeled with I131 has been used as a radiopharmaceutical for adrenal scanning. This material has been prepared for a patient use in our laboratories since 1974. It has recently been determined that this compound is not chemically pure since it undergoes a homoallylic rearrangement to 6 -iodomethyl-19-norcholest-5(10)-en-3 -o1 during its preparation; it was further noted that the rear-ranged product is taken up faster by the adrenals than its parent compound. This is an important advantage of the rearranged 19-iodocholesterol since a dose of one mCi of I131-19-iodocholesterol is needed now to obtain a scan after an interval of 7-10 days. It is planned to prepare pure 6 beta-iodomethyl-norcholest-5(10)-en-3 delta-o1) and to label it with I123 by exchange with Na I123. Considerable changes in the radioiodination have to be worked out due to the short half life of I123 (13 hours). Animal experiments will be carried out in conjunction with the synthesis, in order to determine its possible use in the humans.